VARIABLES AND DATA TYPES

VARIABLES

AND DATA TYPES

Cout statement syntax

cout<<item;

• cout object

• Output operator <<

• Item types:

– Number: integer and float

– Character: printed and non-printed – String

– Expression

– Variable and constants 

Variable

• A variable: is a place in memory that has a name and can hold data

• A variable: is a symbol that represent a storage location in the computer’s memory.

•Its value is the information that stored in the memory in that location.

data

Memory Model:

 Boxes

 Boxes store data

 Addressed boxes

Address

 Variable declaration syntax:

DataType identifier[=initial value];

 Declaring more than one variable:

DataType identifier1[=initial value], identifier2[=initial value], ...;

 Notes:

o [] means optional

oseparate identifiers by commas oone semicolon at the end

Variable

Variable Identifier

To input any data you should define a variable.

DATA ≡ Value Address

≡

Variable ^In

memory

Identifiers

• Identifiers are variable names

•Identifiers naming rules:

o Consists of letters, digits, and the under score character (_)

o Must begin with a letter or underscore.

o Don’t start with a number o No spaces

o No punctuation except underscore

o Don’t use keywords (reserved words): int, float, char, void, main, cout, cin, …….

o C++ is case sensitive—uppercase and lower case letters are different: SALARY is different than salary

Example # 1

The following are legal identifiers in C++.

first

conversion Pay_Rate counter1

Exercise

Are the following identifiers valid?

 Average

 First_Name

 Balanc?e

 3GPA

 Address

 Last name

Data Types

C++ data types fall into three categories

• Simple Data Type.

• Structured Data Type.

• Pointers.

Simple Data Type

C++ simple data can be classified into three categories

1. Integral, which is a data type that deals with integers, or numbers without a decimal part.

2. Floating-point, which is a data type that deals with decimal numbers.

3. Enumeration type, which is a user-defined data type.

Integral data types

1. int Data Type

int identifier ;

-6728, -67, 0, 78, 36782, +763,...

• Defining an integer variable that stores integer numbers

• The memory allocated for the int, unsigned int is 2 to 4 bytes, while the memory allocated for long and unsigned long data types are 4 bytes.

• Positive integers do not necessarily have a + sign in front of them.

• No commas are used within an integer.

Example int num;

long num;

unsigned int num;

2. float Data Types

• Defining a floating-point variable that stores floating point numbers

• Scientific notation

43872918 = 4.3872918 *10^7 {10 to the power of seven}, .0000265 = 2.65 * 10^(-5) {10 to the power of minus five}

47.9832 = 4.7983 * 10^1 {10 to the power of one}

• There are two notation to represent real numbers in C++:

– Decimal notation 35.5 – Exponential notation 3.55E1

float identifier ;

The memory allocated for the float data type is 4 bytes , for the double data type is 8 bytes, and for the long double 10 bytes.

Example

float conversion;

double payRate;

1. Storing Data

Storing data in the computer’s memory is like :

int x = 10 ;

Find place in the memory with size 4 byte As integer

type

Identifier :The name of this place

Optional : the value inside x int x ;

the computer will allocate default value

Storing Data into Variables

In C++ there are two ways that data can be placed into a variable:

1. Initializing Variables

Variables can be initialized when they are declared int first=13, second=10;

float x=12.6;

Equivalently, we can write the following C++ statements.

int first, second;

float x;

first = 13;

second = 10;

x = 12.6;

2. Using C++’s assignment statement

The assignment statement takes the form variable = expression;

The expression is evaluated and its value is assigned to the variable.

In C++, = is called the assignment operator.

3. Use input (read) statements^.

int x = 10; Or int x; Or x=10;

int x;

x=3+7;

Example # 2

int I, J;

I = 4;

J = 8;

I = 7;

J = 5;

cout<<I<<‘ ‘<<J;

4 345

I J

4 8

7 8

7 5

7 5

543 345

I J

Default values

Example # 3

float amountDue;

int counter;

int x, y;

In C++, all identifiers must be declared before they can be used. If we refer to an identifier without declaring it, the compiler will generate an error message indicating that the identifier is not declared.

x=8+3;

int x;

int x;

x=8+3;

Displayin variables

•

• Example:

int a, b, c, d;

a = 65 ; b = 78 ;

cout<<"a"<<endl;

cout<<a<<endl;

cout<<b<<endl;

cout<<c<<'\n';

cout<<d<<endl;

Output a

65 78

6749684 4203005

4. Types of statements

• The body of the main is enclosed between { } and has two types of statements.

• Declaration statements.

• Executable statements.

Declaration Statements

int a, b, c;

float x, y;

Variables (or identifies) can be declared anywhere in the program, but they must be declared before they can be used.

Executable Statements

Example

a = 4; //assignment statement

b = a+1; //equation statement

cout<<a<<endl<<b<<endl; //output statement

5. Form and Style

Consider the following ways of declaring variables.

int feet, inch;

float x, y;

or

int a,b; float x,y; int a,b,float x,y;

or

int feet;

int inch;

float x;

float y;

Blank spaces

int a,b,c;

int a, b, c;

The blanks between the identifiers in the second statement are meaningless.

In the statement,

inta,b,c; Error

no blank between the t and a changes the reserved word int and the identifier a into a new identifier inta.

Example # 4:

• Find the 4 syntax errors .

int x; //Line 1 int a;b; //Line 2

int y //Line 3

Float z; //Line 4 y = w + x; //Line 5

Constants and Variables

• Named Constant: A memory location whose content is not allowed to change during program execution.

• Variable: A memory location whose content may change during program execution.

Named Constant: The syntax to declare a named constant is const dataType identifier = value;

• In C++, const is a reserved word.

Example

const float conversion = 2.54;

const int noOfStudents = 20;

const float payRate = 15.75;

noOfStudents = 15;

Naming Identifiers

float a = 2.54; //conversion constant

float x; //variable to hold centimeters float y; //variable to hold inches

x = y * a;

Consider the following

float conversion = 2.54;

float centimeters;

float inches;

centimeters = inches * conversion;

Note: Use meaningful identifiers